1. Field of the Invention
The present invention is directed to a method and apparatus for preparing catalyst pellets of uniform preselected length.
2. Description of the Prior Art
Catalyst pellets may be prepared by mixing an inert carrier such as clay, alumina, carbon, etc., with or without an active catalyst component so as to form a mulled mixture. The resulting mixture is then extruded through dies having a nominal diameter of generally from about 1/32" to about 1/4" in diameter. During extrusion the strands break off in a non-uniform length while dropping to a conveyor belt en route to a dryer, usually a rotating tray dryer. Following the dryer, the strands are passed over a sizing screener where all material over, and sometimes under, a preselected length is rejected from the product stream to be discarded and/or further reduced in length.
Another method comprises extruding the catalyst extrudate through dies to produce the so-called "longs". These longs are charged to a ribbon blender where the strand lengths are reduced by attrition. This procedure results in non-uniform catalyst strands and the production of an excessive amount of fines which are generally unrecoverable. Such waste and further handling may account to as much as 50% of the stream, which is excessive.
It is therefore desirable to be able to produce catalyst pellets having a relatively uniform length from strands in high yield with a concommittant reduction in the production of unusable fines.
An apparatus and method has now been discovered wherein catalyst strands are uniformly sized to a preselected length without the production of an excessive amount of fines.